The present invention relates to spinal implants, devices for anchoring, and methods for implantation of, such implants in an intervertebral disc space.
The intervertebral disc functions to stabilize the spine and to distribute forces between vertebral bodies. A normal disc includes a gelatinous nucleus pulposus, an annulus fibrosis and two vertebral end plates. The nucleus pulposus is surrounded and confined by the annulus fibrosis.
Intervertebral discs may be displaced or damaged due to trauma or disease. Disruption of the annulus fibrosis allows the nucleus pulposus to protrude into the spinal canal, a condition commonly referred to as a herniated or ruptured disc. The extruded nucleus pulposus may press on the spinal nerve, which may result in nerve damage, pain, numbness, muscle weakness and paralysis. Intervertebral discs may also deteriorate due to the normal aging process. As a disc dehydrates and hardens, the disc space height will be reduced, leading to instability of the spine, decreased mobility and pain.
One way to relieve the symptoms of these conditions is by surgical removal of a portion or all of the intervertebral disc. The removal of the damaged or unhealthy disc may allow the disc space to collapse, which could lead to instability of the spine, abnormal joint mechanics, nerve damage, as well as severe pain. Therefore, after removal of the disc, adjacent vertebrae are typically fused to preserve the disc space.
Several devices exist to fill an intervertebral space following removal of all or part of the intervertebral disc in order to prevent disc space collapse and to promote fusion of adjacent vertebrae surrounding the disc space. Even though a certain degree of success with these devices has been achieved, full motion is typically never regained after such intervertebral fusions. Attempts to overcome these problems has led to the development of disc replacements. Many of these devices are complicated, bulky and made of a combination of metallic and elastomeric components and thus never fully return the full range of motion desired. More recently, efforts have been directed to replacing the nucleus pulposus of the disc with a similar gelatinous material, such as a hydrogel. However, once positioned in the disc space, many hydrogel implants may migrate in the disc space and/or may be expelled from the disc space through an annular defect. Closure of the annular defect, or other opening, using surgical sutures or staples following implantion is typically difficult and, in some cases, ineffective. Moreover, such hydrogel implants may be subject to extensive deformation. Additionally, such hydrogel implants typically lack mechanical strength at high water content and are therefore more prone to excessive deformation, creep, cracking, tearing or other damage under fatigue loading conditions.
A need therefore exists for more durable nucleus pulposus or other spinal implants, including implants that are less resistant to deformation, as well as devices and methods that anchor the implants so that the implants are more resistant to migration and/or expulsion through an opening in the annulus fibrosis. The present invention addresses these needs.
Devices for anchoring a spinal implant in an intervertebral disc space are provided. In one form of the invention, a device includes an elongated anchoring body, such as an anchoring rod, and at least one securing member attached to the anchoring rod. The anchoring body or rod is configured to anchor, hold, or otherwise retain a spinal implant. In certain forms of the invention wherein more than one securing member is included, the securing members are spaced apart along the length of the anchoring rod and may define a region for disposing an implant therebetween. The anchoring rod has a first end and a second end, wherein the first end is securable to an adjacent vertebra. The anchoring devices may be made from metallic materials, non-metallic materials and combinations thereof.
Spinal implant systems are also provided that include the anchoring device described above and an elastic spinal implant. In certain forms of the invention, the anchoring devices include an anchoring rod and at least one securing member attached to the anchoring rod. The anchoring rod includes a first end, a second end, a longitudinal axis and extends at least partially through the implant. The anchoring component is securable to an adjacent vertebra. In one form of the invention, the securing members may be external to the implant, while in other forms of the invention the securing members may be internal to the implant or may be both internal and external to the implant.
Spinal implants are also provided that are resistant to lateral deformation as they are restrained, or otherwise reinforced, by a flexible, peripheral supporting band. In one form of the invention, the implant includes an elastic body sized for introduction into the intervertebral disc space. The elastic body includes an upper surface and a lower surface for contacting adjacent vertebral endplates. A flexible peripheral supporting band is disposed circumferentially about the elastic body to reduce deformation of the body. At least a portion of the upper and lower surfaces of the elastic body are free of the supporting band. The implant, including the band, is sized to fit within an intervertebral disc space which is at least partially defined by an annulus fibrosis.
Methods of anchoring a spinal implant are also provided. A preferred method includes providing an elastic spinal implant and an anchoring component that includes the anchoring devices described above, extending the anchoring rod of the device at least partially through the implant, and securing the anchoring component to an adjacent vertebra.
Methods of reducing deformation of a spinal implant are also provided. In one embodiment, a method includes disposing a flexible peripheral supporting band circumferentially about the implants described above.
One object of the present invention is to provide devices for anchoring spinal implants so they will be resistant to excessive migration in, and/or expulsion from, the intervertebral disc space.
Yet another object of the invention is to provide spinal implant systems including an elastic spinal implant and an anchoring component for anchoring the implant.
A further object of the invention is to provide spinal implants that are more resistant to lateral deformation.
These and other objects and advantages of the present invention will be apparent from the descriptions herein.